Abstract
Artificial propagation programs focused on production, such as commercial aquaculture or forestry, entail strong domestication selection. Spillover from such programs can cause unintended fitness and demographic consequences for wild conspecifics. The range of possible management practices to minimize such consequences vary in their control of genetic and demographic processes. Here, we use a model of coupled genetic and demographic dynamics to evaluate alternative management approaches to minimizing unintended consequences of aquaculture escapees. We find that, if strong natural selection occurs between escape and reproduction, an extremely maladapted (i.e., nonlocal-origin, highly domesticated) stock could have fitness consequences analogous to a weakly diverged cultured stock; otherwise, wild population fitness declines with increasing maladaptation in the cultured stock. Reducing escapees through low-level leakage is more effective than reducing an analogous number of escapees from large, rare pulses. This result arises because low-level leakage leads to the continual lowering of wild population fitness and subsequent increased proportional contribution of maladapted cultured escapees to the total population. Increased sterilization efficacy can cause rapid, nonlinear reductions in unintended fitness consequences. Finally, sensitivity to the stage of escape indicates a need for improved monitoring data on how the number of escapees varies across life cycle stages.
Highlights
Cultivation of organisms for production purposes such as agriculture, livestock, forestry, and aquaculture inevitably involves strong artificial selection, both intentional and unintentional, on a variety of morphological, physiological, behavioral, and life-history traits (Ledig 1992; MignonGrasteau et al 2005; Hutchings and Fraser 2008)
Degree of maladaptation The potential consequences of increasing maladaptation in the aquaculture environment depend on the relative timing of natural selection, escape, and reproduction in the life cycle (Fig. 2)
Our results indicate a potential need for greater attention to the role of low-level leakage in driving unintended fitness consequences of aquaculture escapees
Summary
Cultivation of organisms for production purposes such as agriculture, livestock, forestry, and aquaculture inevitably involves strong artificial selection, both intentional and unintentional, on a variety of morphological, physiological, behavioral, and life-history traits (Ledig 1992; MignonGrasteau et al 2005; Hutchings and Fraser 2008). Commercial commodity aquaculture (i.e., full life cycle rearing with a goal of complete capture for production; Lorenzen et al 2012; Utter and Epifanio 2002) exemplifies this potential for cultivation to affect the fitness of wild populations. Many aquaculture programs involve growth of the cultured individuals in semi-closed facilities, such as net pens, that are located in the same freshwater, marine, or estuarine environment as conspecifics, such that spillover has the potential to affect the fitness and dynamics of wild populations (Youngson et al 2001; Naylor et al 2005; Hutchings and Fraser 2008; Jensen et al 2010; Lorenzen et al 2012)
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